1. Field of the Invention
The present invention relates to a channel separating filter apparatus, a Phase Shift Keying (referred to as a PSK hereinafter) demodulator apparatus and a PSK receiver apparatus, and in particular, to a channel separating filter apparatus for separating a frequency-multiplexed signal comprised of channel signals into a plurality of channel signals, a PSK demodulator apparatus constituted by using the channel separating filter apparatus, and a PSK receiver apparatus constituted by using the channel separating filter apparatus.
2. Description of the Prior Art
In a personal handy phone system (referred to as a PHS system hereinafter) which is so-called a simple type portable telephone system, as shown in FIG. 20A, a band using one carrier wave is used for one base station. In this case, a time division multiplex access-time division duplex system (referred to as a TDMA-TDD system hereinafter) is used, where three mobile terminals can be simultaneously used at maximum per base station. In an actual PHS system, a channel for line control is necessary, and therefore, as shown in FIG. 20B, so-called ping-pong transmission is executed by using four channels in one direction.
In order to increase the number of terminals within one service area 110 in a prior art PHS system, a plurality of carrier waves CA1, CA2 and CA3 are used as shown in FIGS. 21A and 21B. In other words, the number of base stations using one carrier wave is increased to a plural number or more within one service area. In this case, with regard to the frequency of the carrier wave used by each base station, an unoccupied channel out of pre-allocated 77 channels is used in the case of outgoing call from the base station or in the case of incoming call to a mobile terminal station. Furthermore, in the prior art PHS system, a band-pass filter is used for separation of channels, and a delay detection method or differential coherent detection method is widely used for demodulation of a signal modulated by a .pi./4-shift QPSK (Quadrature Phase Shift Keying) method.
However, when a band-pass filter is used for separation of channels in a radio system using frequency-multiplexed channels, an inductance circuit is used in the band-pass filter. Therefore, there are the following problems:
(a) the size of the circuit thereof becomes larger; PA1 (b) the manufacturing cost thereof becomes relatively expensive; and PA1 (c) it is difficult to adjust the center frequency of the pass-band. PA1 frequency-converting means for frequency-converting the frequency-multiplexed signal into a plurality of channel signals, so that an average value of carrier wave frequencies of two channel signals which are located in a center of the frequency-multiplexed signal and are adjacent to each other becomes substantially zero, and for outputting the plurality of frequency-converted channel signals; and PA1 channel separating means for separating the plurality of frequency-converted channel signals outputted from said frequency-converting means into respective channel signals each having only a frequency component of each channel signal, PA1 wherein said channel separating means comprises at least first stage filter bank, and PA1 wherein said first stage filter bank comprises: PA1 wherein said second stage filter bank comprises: PA1 first detecting means for detecting a signal level of the second signal outputted from said first processing means and for outputting a first detection signal when no second signal exists; PA1 second detecting means for detecting a signal level of the fourth signal outputted from said second processing means and for outputting a second detection signal when no fourth signal exists; and PA1 operation control means, in response to the first detection signal outputted from said first detecting means, for controlling said second positive pass filter, said second negative pass filter and said third and fourth processing means to stop operations of said second positive pass filter, said second negative pass filter and said third and fourth processing means, and further, in response to the second detection signal outputted from said second detecting means, for controlling said third positive pass filter, said third negative pass filter and said fifth and sixth processing means to stop operations of said third positive pass filter, said third negative pass filter and said fifth and sixth processing means. PA1 further frequency-converting means for frequency-converting the PSK-modulated signal into a frequency-converted PSK-modulated signal, so that a center frequency of the PSK-modulated signal becomes substantially zero, and for outputting the frequency-converted PSK-modulated signal; and PA1 wherein said signal demodulating means comprises at least first stage filter bank, and PA1 wherein said first stage filter bank comprises: PA1 further frequency-converting means for frequency-converting the PSK-modulated signal into a frequency-converted PSK-modulated signal, so that a center frequency of the PSK-modulated signal becomes substantially zero, and for outputting the frequency-converted PSK-modulated signal; and PA1 signal demodulating means for demodulating the frequency-converted PSK-modulated signal outputted from said further frequency-converting means so as to generate a demodulated signal representing one code, and for outputting the generated demodulated signal, PA1 wherein said signal demodulating means comprises at least first and second stage filter bank, PA1 wherein said first stage filter bank comprises: PA1 first detecting means for detecting a signal level of the second signal outputted from said first processing means, and for outputting a first detection signal when no second signal exists; PA1 second detecting means for detecting a signal level of the fourth signal outputted from said second processing means, and for outputting a second detection signal when no fourth signal exists; and PA1 operation control means, in response to the first detection signal outputted from said first detecting means, for controlling said second positive pass filter, said second negative pass filter, and said first and second code discriminating means to stop operations of said second positive pass filter, said second negative pass filter, and said first and second code discriminating means, and further, in response to the second detection signal outputted from said second detecting means, for controlling said third positive pass filter, said third negative pass filter and said third and fourth code discriminating means to stop operations of said third positive pass filter, said third negative pass filter and said third and fourth code discriminating means. PA1 receiving means for receiving a radio signal of a frequency-multiplexed signal comprised of channel signals each being a PSK-modulated signal; PA1 a channel separating filter apparatus for separating the radio signal received by said receiving means into respective channel signals; and PA1 a PSK demodulator apparatus for demodulating the respective channel signals separated by said channel separating filter apparatus so as to generate respective demodulated channel signals, and for outputting the generated respective demodulated channel signals, and PA1 wherein said channel separating filter apparatus comprises: PA1 wherein said second stage filter bank comprises: PA1 first detecting means for detecting a signal level of the second signal outputted from said first processing means and for outputting a first detection signal when no second signal exists; PA1 second detecting means for detecting a signal level of the fourth signal outputted from said second processing means and for outputting a second detection signal when no fourth signal exists; and PA1 operation control means, in response to the first detection signal outputted from said first detecting means, for controlling said second positive pass filter, said second negative pass filter and said third and fourth processing means to stop operations of said second positive pass filter, said second negative pass filter and said third and fourth processing means, and further, in response to the second detection signal outputted from said second detecting means, for controlling said third positive pass filter, said third negative pass filter and said fifth and sixth processing means to stop operations of said third positive pass filter, said third negative pass filter and said fifth and sixth processing means. PA1 receiving means for receiving a radio signal of a frequency-multiplexed signal comprised of channel signals each being a PSK-modulated signal; PA1 a channel separating filter apparatus for separating the radio signal received by said receiving means into respective channel signals; and PA1 a PSK demodulator apparatus for demodulating the respective channel signals separated by said channel separating filter apparatus so as to generate respective demodulated channel signals, and for outputting the generated respective demodulated channel signals, PA1 wherein said PSK demodulator apparatus demodulates a PSK-modulated signal modulated according to at least two codes, and PA1 wherein said PSK demodulator apparatus comprises: PA1 further frequency-converting means for frequency-converting the PSK-modulated signal into a frequency-converted PSK-modulated signal, so that a center frequency of the PSK-modulated signal becomes substantially zero, and for outputting the frequency-converted PSK-modulated signal; and PA1 signal demodulating means for demodulating the frequency-converted PSK-modulated signal outputted from said further frequency-converting means so as to generate a demodulated signal representing one code, and for outputting the generated demodulated signal, PA1 wherein said signal demodulating means comprises at least first stage filter bank, and PA1 wherein said first stage filter bank comprises: PA1 further frequency-converting means for frequency-converting the PSK-modulated signal into a frequency-converted PSK-modulated signal, so that a center frequency of the PSK-modulated signal becomes substantially zero, and for outputting the frequency-converted PSK-modulated signal; and PA1 signal demodulating means for demodulating the frequency-converted PSK-modulated signal outputted from said further frequency-converting means so as to generate a demodulated signal representing one code, and for outputting the generated demodulated signal, PA1 wherein said signal demodulating means comprises at least first and second stage filter bank, PA1 wherein said first stage filter bank comprises: PA1 first detecting means for detecting a signal level of the second signal outputted from said first processing means, and for outputting a first detection signal when no second signal exists; PA1 second detecting means for detecting a signal level of the fourth signal outputted from said second processing means, and for outputting a second detection signal when no fourth signal exists; and PA1 operation control means, in response to the first detection signal outputted from said first detecting means, for controlling said second positive pass filter, said second negative pass filter, and said first and second code discriminating means to stop operations of said second positive pass filter, said second negative pass filter, and said first and second code discriminating means, and further, in response to the second detection signal outputted from said second detecting means, for controlling said third positive pass filter, said third negative pass filter and said third and fourth code discriminating means to stop operations of said third positive pass filter, said third negative pass filter and said third and fourth code discriminating means.
Furthermore, the use of the delay detection method or differential coherent detection method when demodulating a signal modulated by .pi./4-shift QPSK has been accompanied by such a problem that it is necessary to provide a relatively complicated circuit.